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Heat Recovery Units Again

As the heat continues here in Cent FL, I continue to wonder why heat recovery units on A/Cs and heat pumps continue to be ignored. Most A/C pros dismiss them offhand saying 'they don't work with high efficiency units' but they most certainly work with 13 SEER systems and lower compressor draw about 20%. Easy to measure with an amprobe and a switch to turn the HRU circulator pump on and off. Another complaint I've heard is that local water quality affects the circulator pumps but that would also be a problem with solar hot water heaters...people just need to know that an HRU may need some maintenance just like a solar system does. At least you don't have the big panels cluttering up your roof and becoming an issue when the roof is replaced. I feel that solar hot water in Florida is a huge, costly mistake as opposed to a HRU. Any solar fans want to scrap on that comment? I've had experience with 3 HRU's (one on a 7 SEER York that was recently replaced with a 13 SEER Ducane, another 13 and a 10) and all have cut electric bills at least $30 a month..usually more. Easy to tell if the unit needs work...your power bill goes up. I know I'd never have a house in Florida without one. Can anyone give me reasons not to use them other than anecdotal evidence? The money you save 'downgrading' from a 15 to a 13 SEER system more than pays for the HRU and the HRU will add the efficiency points back into the system....plus give free hot water. Interestingly enough, once you have one, you begin to see using hot water is cheaper than using cold...the more heat you shed, the more efficient the A/C becomes. I made sure to install a recirculating loop for my hot water...the HRU pump provides instant hot water throughout the house (saving me more money as it dissapates more heat) . Also clothes always clean better in hot water...My next idea is installing a mixing valve to dump a little hot water into my sprinkler system. I don't see where watering with slightly warm water will be a problem and should cut the power bill some more...

We have several older HRU's in our area, 90% of them have the impeller all disentigrated, not faulting them. When we approach customers to have these repaired, it is always a firm "no" they just dont seem to think it does anything for them, and have very little knowledge of what it even does. We have not installed any with new equipment that I can remember, and alot of them get disconnected on change-outs. I agree they are useful, but for some reason hard to convince people.

I have one on a dual capacity carrier unit but had to jump out the H/P low ambient klixon. I cannot do that on a customer's system.
Quite a few customers that have them don't know it so they don't take advantage of the savings.

For my customers my absolute biggest reason for not continuing to install them is concern with reliabilty now that most of the equipment we install is R410a.

It's an old study but,

Measured Performance of Water Heating Systems

The electrical demand in 80 houses using four different hot water systems has been investigated. Twenty systems of each type were monitored from 1982 - 1984 in locations in South, Central and North Florida: conventional electric resistance, heat pump water heaters, de-superheater heat recovery units and solar hot water heaters [5]. Data was taken at 15-minute intervals so that time-of-day electrical demand data was available. Average annual hot water electricity consumption for conventional electric resistance systems was 3,030 kWh with a measured efficiency of 82%. Each conventional electric resistance heater was found to add an average of 0.3 kW to coincident electric demand form 5 - 6 PM on peak summer days. Solar systems reduced coincident summer peak demands by at least 0.2 kW and provided approximately 70% of annual hot water needs with a total electrical demand of only 980 kWh. Figure 2A and 2B contrasts the peak summer day aggregate load shape of the two system types which evidence rather dramatic differences. De-superheater systems provided useful reductions to peak summertime demand, but only marginally better performance than resistance systems for overall annual energy use. Heat pump water heaters performed with an annual efficiency of 153%, but only provided modest reductions to summer coincident peak demand.

U of F study

Adrien...Google 'university of florida EES-26' for an interesting study of HRU's with a lot of good formulas to examine. I'd have to take exception to the study you are quoting as here in cent Fl, we use AC 9 months of the year and the 80 gallon water heater we have as a storage tank is shut off for that time and we never run short of hot water. I'm not sure in Florida whether the klixon you mention ever comes into play as I've never seen the compressor discharge temp below 180 degrees (I'd NEVER think of testing the temp of that little pipe by touching it...hehehe) . Even in the winter time I get hot water although the heat pump is no doubt running longer to heat the house.

HRU are inconsistant on higher seer units. The brands we have used require field modification to generate hot water. Since the alteration voids the Listed and Approved ratings I do not care for that liability exposure. So lets agree to disagree and move on.

I know that if there is a heat recovery on a Carrier/Bryant/Payne unit. It voids the compressor warranty on it. I'm not sure about the other manufacturers, but I would think its probably not too far off. They are also expensive to install. Particularly if you are retrofitting it into and existing house. You have to re-do plumbing to hot water heater as well as refrigerant lines. That's not including the cost of the unit itself. I would simply put a timer on my hot water heater to turn it off during hours which you will not be using it. Like during the middle of the day and middle of the night.